Summary information |
|
|---|---|
Default value |
1 |
Range of values |
1–128 |
Status |
Static |
Display level |
Intermediate |
Required role |
System Administrator |
The role of max online engines is to set a high value of engines to be taken online at any one time in an SMP environment. It does not take the number of CPUs available at start-up into account, and allows users to add CPUs at a later date.
max engines online specifies the maximum number of Adaptive Server engines that can be online at any one time in an SMP environment. See Chapter 20, “Managing Multiprocessor Servers,” for a detailed discussion of how to set this parameter for your SMP environment.
At start-up, Adaptive Server starts with a single engine and completes its initialization, including recovery of all databases. Its final task is to allocate additional server engines. Each engine accesses common data structures in shared memory.
When tuning the max engines online parameter:
Never have more online engines than there are CPUs.
Depending on overall system load (including applications other than Adaptive Server), you may achieve optimal throughput by leaving some CPUs free to run non-Adaptive Server processes.
Better throughput can be achieved by running fewer engines with high CPU use, rather than by running more engines with low CPU use.
Scalability is application-dependent. You should conduct extensive benchmarks on your application to determine the best configuration of online engines.
You can use the dbcc engine command to take engines offline or to bring them online line. You can offline all engines other than engine zero.
See “Taking engines offline with dbcc engine” for information on using dbcc engine. See Chapter 4, “Using Engines and CPUs” in the Performance and Tuning: Basics for more information on performance and engine tuning.
